This filter allows you to specify the ratio of followers to followings.

This can help include / ignore profiles that have large discrepancies between their followings / followers. For example, someone who has 10,000 followers but is following 10, isn't going to follow you back.

The Ratio
Followers / Followings.

i.e.
10,000 / 10
= ratio 10

If a user has 1000 followers and is following 800
1000 / 800
= ratio: 1.25

If a user has 100 followers and is following 100
100/100
= ratio: 1

if a user has 1000 followers and is following 2000

1000/2000
= ratio: 0.5

So with this feature you can know whether a user is following the same number of users that follows them, thus is a good candidate for a follow back